I. Field of the Present Invention
The present invention relates generally to fluid circuits for regulating the supply of pressurized fluid to a fluid actuated tool, and more particularly to such circuits in which the pressure of the fluid is regulated by controlling an electrical signal delivered to an electro-pneumatic transducer.
II. Description of the Prior Art
Fluid powered tools such as pneumatic wrenches and others utilizing hydraulic cylinders must often be operated at precise fluid pressures in order to perform desired operations. For example, the torque generated by a pneumatic wrench corresponds with the pressure of air delivered to the wrench. Similarly, the force imparted by a hydraulic cylinder directly corresponds with the pressure of fluid supplied to the cylinder. Although manually operated mechanical pressure regulators are well known, they are not well adapted for making repeated adjustments to the pressure applied to a tool which may be necessary during assembly line operations. Moreover, manual adjustment of these regulators can affect the accuracy of the pressure being applied to the tool, especially when repeated adjustments of the pressure are necessary. Moreover such pressure regulators cannot automatically be adjusted and can substantially increase the labor and time necessary to make variations in the pressure applied to hydraulic or pneumatic tools.
Some of the above mentioned disadvantages have been overcome by the use of current to pressure (I/P) transducers which discharge fluid under a pressure corresponding to the value of a current signal applied to the transducer. However, such transducers accurately vary the output pressure only through a limited range, and may therefore be inappropriate for use in industrial applications where broad ranges of repeated pressure variations are necessary.
A system for utilizing electrical control signals for establishing a predetermined output pressure is disclosed in pending U.S. patent application Ser. No. 626,379 of the same inventor. In such a system, the output pressure applied to a welding tool continuously varies as the control signal varies. However, while the change in output pressure occurs relatively quickly, there is some time lag between the time at which the control signal is applied until the time that the tool output is stabilized at the desired value. Thus, the tool may be momentarily operated at an undesirably high or low pressure. Moreover, although the system can be calibrated so that there is precise correspondence between the output pressure and the electrical control signal, the system does not disclose any means for checking the output pressure actually being delivered to the tool or for making a record of the output pressure changes occuring during an operating period. In addition, the system disclosed in that patent application does not teach or suggest an apparatus for regulating the pressure delivered to a plurality of tools from a single computerized control unit such as a microprocessor.